Process control systems for industrial processes, whether distributed control system (DCS) or supervisory control and data acquisition (SCADA) systems, generally include one or more process controllers communicatively coupled to at least one host (e.g., an operator workstation) and to one or more process control devices (e.g., field devices) configured to communicate via analog, digital or combined analog/digital communication signals and/or protocols. Such process control systems are commonly used in oil and gas, chemical, pharmaceutical, pulp and paper manufacturing and petroleum processes.
The field devices can comprise device controllers, valves, valve actuators or positioners, switches, transmitters (e.g. temperature, pressure, level, flow rate, or chemical composition sensors), performing functions within the process control system such as actuator opening and/or closing valves and gauges or sensors measuring process parameters. The process controller receives signals indicative of process measurements made by the field devices and/or other information pertaining to the field devices, uses this information to implement a control routine, and generates control signals over buses and/or other communication lines to the field devices such as actuators to control the operation of the processing equipment of the process control system.
To provide improved modularity and inter-manufacturer compatibility process controls manufacturers have moved toward decentralization of control within a process by using ‘smart’ field devices that communicate generally using a serial protocol such as the HART®, PROFIBUS®, WORLDFIP®, Device-Net®, CAN, and Foundation™ Fieldbus (hereinafter “Fieldbus”) protocols. These smart field devices are microprocessor-based devices such as sensors, that in some cases, such as with Fieldbus devices, also perform control loop functions traditionally executed by a Distributed Control System (DCS) controller. Because smart field devices provide control capability and communicate using an open protocol, smart field devices from a variety of different manufacturers can typically communicate with one another via a common digital data bus and can interoperate to execute a control loop without the intervention of a DCS controller.
Some industrial automation systems may include a portion of their communications according to the open process control (OPC) Unified Architecture (UA) protocol. OPC UA is an open (non-proprietary) standard for manufacturer-independent data communications which can be machine-to-machine or between applications. OPC UA is primarily used in industrial automation systems and is specified by the OPC Foundation. For example, an industrial automation system may include a gateway device that converts serial protocol data received from the field devices to OPC UA data that is coupled to an OPC UA server which may also make this information available via a network connection to one or more OPC clients operating at another location. The OPC UA clients may utilize OPC UA service calls over a network connection in order to send OPC UA data to and receive OPC UA data from an OPC UA server(s).